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Home page > Animal Kingdom > Echolocation of Bats

ECHOLOCATION of BATS
Animal Kingdom


Bats are very interesting creatures. The most intriguing of their abilities is their extraordinary faculty of navigation.
The echolocative ability of bats was discovered through a series of experiments conducted by scientists. Let us take a closer look at these experiments in order to unveil the extraordinary design of these creatures:1
In the first of these experiments, a bat was left in a completely dark room. On one corner of the same room, a fly was placed as a prey for the bat. From then on, everything taking place in the room was monitored with night vision cameras. As the fly started to take into the air, the bat, from the other corner of the room, swiftly moved directly to where the fly was and captured it. Through this experiment, it was concluded that the bats had a very sharp sense of perception even in complete darkness. However, was this perception of the bat due to the sense of hearing? Or, was it because it had night vision?
In order to answer these questions, a second experiment was carried out. In a corner of the same room a group of caterpillars were placed and covered under a sheet of newspaper. Once released, the bat did not lose any time in lifting the newspaper sheet and eating the caterpillars. This proved that the navigational faculty of the bat has no relationship with the sense of vision.


Experiments show that bats are able to easily locate and fly through the passageways in the walls even in complete darkness.

Scientists continued with their experiments on bats: a new experiment was conducted in a long corridor, on one side of which was a bat and on the other a group of butterflies. In addition, a series of partition walls were installed perpendicular to the sidewalls. In each partition, there was a single hole just big enough for the bat to fly through. These holes, however, were located in a different spot on each partition. That is, the bat had to zigzag its way through them.
Scientist started their observations as soon as the bat was released into the pitch darkness of the
corridor. When the bat came to the first partition it located the hole easily and passed right through it. The same was observed at all partitions: the bat appeared not only to know where the partition was but also where exactly the hole was. After going through the last hole, the bat filled its stomach with its catch.

Absolutely stunned by what they observed, the scientists decided to conduct one last experiment in order to understand the sensitivity of the bat's perception. The goal this time was to determine the bat's perceptual limits more clearly. Again, a long tunnel was prepared and steel wires of 3/128-inch (0.6 mm) diametre were hung from ceiling to floor and placed randomly throughout. Much to the observers' astonishment, the bat completed its journey without tripping over a single obstacle. This flight showed that the bat is able to detect obstacles of as little as 3/128-inch (0.6 mm) thickness. The research that followed revealed that the bat's incredible perceptual faculty is linked to their echolocation system. Bats radiate high frequency sounds in order to detect objects around them. The reflection of these sounds, which are inaudible to humans, enables the bat to get a "map" of its environment.2 That is, the bat's perception of a fly is made possible by the sounds reflected back to the bat from the fly.
An echolocating bat registers each outgoing sound pulse and compares the originals to returning echoes. The time lapsed between generating the outgoing sound and receiving an incoming echo provides an accurate assessment of a target's distance from the bat. For example, in the experiment where the bat caught the caterpillar on the floor, the bat perceived the caterpillar and the shape of the room by emitting high pitch sounds and detecting the reflected signals. The floor reflected the sounds; hence, the bat determined its distance from the floor. On the contrary, the caterpillar was about 3/16-inch (0.5 cm) to 3/8-inch (1 cm) closer to the bat than was the ground. In addition, it made minute moves and this, in turn, changed the reflected frequencies. This way, a bat could detect the presence of a caterpillar on the floor. It emitted about twenty thousand cycles in a second and could analyse all the reflected sounds. Furthermore, while it carried out this task, the bat itself travelled. Careful consideration of all these facts clearly reveals the miraculous design in their creation.
Another stunning feature of bats' echolocation is the fact that the hearing of bats has been created such that they cannot hear any other sounds than their own. The spectrum of frequencies audible to these creatures is very narrow, which would normally create a great problem for the animal because of the Doppler Effect. According to the Doppler Effect, if the source of sounds and the receiver of sounds are both relatively stationary, the receiver will detect the same frequency as the source emits. However, if one or the other is moving, the detected frequency will be different than the emitted frequency. In this case, the frequency of the reflected sound could fall into the spectrum of frequencies inaudible to the bat. The bat, therefore, faces the potential problem of not being able to hear the echoes of its sounds from a fly that moves away.

 

BAT
(Eptesicus)

RADAR
(SCR-268)

RADAR
(AN/APS-10)

SONAR
QCS-T

Weight of system (kg)

0.01200

12,000

90

450

Peak Power Output (W)

0.00001

75,000

10,000

600

Diametre of Target (m)

0.01000

5

3

5

Echolocation Efficiency Index

2x109

6x10-5

3x10-2

2x10-3

Relative Figure of Merit

1

3x10-14

1,5x10-11

10-12

The system used by bats to locate their prey is millions of times more efficient and accurate than manmade radar and sonar. The table above clearly illustrates these properties. "Echolocation efficiency index" is range divided by the product weight times power times target diametre. "Relative figure of merit" compares the echolocation efficiency indexes with the bat as 1.

Nevertheless, this is never a problem for the bat because it adjusts the frequency of sounds that it sends towards moving objects as if it knows about the Doppler Effect. For instance, it sends the highest frequency sounds to a fly moving away so that the reflections are not lost in the inaudible section of the sound spectrum.
So, how does this adjustment take place?
In the brain of the bat, there are two kinds of neurons (nerve cells) that control its sonar systems; one perceives the reflected ultrasound and the other commands the muscles to produce echolocation calls. These two neurons work in such complete synchrony that a minute deviation in the reflected signals alerts the latter and provide the frequency of the call to be in tune with the frequency of the echo. Hence, the pitch of the bat's ultrasound changes in accordance with its surroundings for maximum efficiency.
It is impossible to overlook the blow that this system deals to the explanations of the theory of evolution through coincidence. The sonar system of bats is extremely complex in nature and cannot be explained by evolution through arbitrary mutations. The simultaneous existence of all components of the system is vital for its functionality. The bat has not only to release high pitch sounds but also to process reflected signals and to manoeuvre and adjust its sonar squeals all at the same time. Naturally, all of this cannot be explained by coincidence and can only be a sure sign of how flawlessly God created the bat.

The largest bat colony on earth, with a population reaching 50 million, lives in America. Freetails ride 60 mph (95 km/h), and fly as high as 10,000 feet (3050 metres). It is so large that it can be easily observed by airport radar.3

It is discovered that bats wander in many different ways once they leave their cave. However, they always fly back to it on a straight route from wherever they are. It is still not clear how they are able to navigate the return journey to the cave.

Scientific research further reveals new examples of the miracles of creation in bats. Through each new miraculous discovery, the world of science attempts to understand how these systems work. For example, new research on bats has had very interesting findings in recent years.4

A few scientists, who wanted to examine a group of bats living in a certain cave, installed transmitters on some of the group members. Bats were observed to leave the cave at night and feed outside until dawn. Researchers kept detailed records of these journeys. They discovered that some bats travelled as far as 30-45 miles (50-70 kilometres) from the cave. The most astonishing finding was the return flight, which started shortly before sunrise. All bats flew straight back to the cave from wherever they were. How can bats know where they are and how far away they are from their caves?
We do not yet have detailed knowledge of how they navigate their return flight. Scientists do not believe the auditory system to have a big impact on the return journey. Reminding us that bats are completely blind to light, scientists expect to encounter another surprising system. In short, science continues to discover new miracles of creation in the bats.

References:

1. J. A. Summer, Maria Torres, Scientific Research about Bats, Boston: National Academic Press, September 1996, pp. 192-195.
2. Donald Griffin, Animal Engineering, San Francisco, The Rockefeller University - W.H. Freeman Com., pp. 72-75. 3. Merlin D. Tuttle, "Saving North America’s Beleaguered Bats", National Geographic, August 1995, p. 40.
3. Merlin D. Tuttle, "Saving North America’s Beleaguered Bats", National Geographic, August 1995, p. 40.
4. J. A. Summer, Maria Torres, Scientific Research about Bats, pp. 192-195

 
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